Hypergolic method of operating a bipropellant liquid reaction motor using difluoroamino compounds



United States Patent 3,442,081 HYPERGOLIC METHOD OF OPERATING A BI- PROPELLANT LIQUID REACTION MOTOR USING DIFLUOROAMINO COMPOUNDS Orval E. Ayers and Chester W. Huskins, Huntsville, Ala., and Bert T. Fant, Baton Rouge, La., assignors to the United States of America as represented by the Secretary of the Armv No Drawing. Filed Feb. 27, 1963, Ser. No. 261,545 Int. Cl. F23 1/02; C06c /08 US. Cl. 60212 18 Claims The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to liquid propellants and more particularly to a method of operating a bipropellant liquid reaction motor.

The propelling action of a rocket motor comes from the generation of large quantities of gases by the chemical reaction of suitable propellants within the rocket motor. The propellants used in a rocket motor may be a solid or a liquid rnonopropellant (materials containing an adequate supply of available oxygen in their chemical composition), or two liquids (fuel plus oxidizer).

The essential elements of a bipropellant liquid rocket engine are a combustion chamber, exhaust nozzle, propellant injection system, fuel tank, oxidant tank, and control valves. The fuel and oxidant react in the combustion chamber to form high temperature gases at pressures governed by the nozzle throat area, rate of propellant injection, ratio of fuel to oxidant, and the efliciency of conversion. Combustion temperature and thus pressure are also functions of the fuel and oxidant used. These high temperature gases are accelerated by a nozzle to a very high velocity. The reaction force resultant to this acceleration of gas provides thrust to drive the rocket.

The injection system through which the liquid propellants flow into the combustion chamber is usually designed to mix the propellants as they enter. Any liquids which are capable of rapid combustion may be used as liquid propellants to drive rockets. However, for some propellants it is necessary to have a preheating device or electrical igniter in the system. Other propellants ignite spontaneously on contact with the oxidizer at normal temperatures. These propellant fuels are called hypergolic fuels.

Accordingly it is an object of this invention to provide an improved method of operating a liquid bipropellant motor.

A further object of the invention is to provide an improved method of operating a 'bipropellant liquid motor wherein the fuel and oxidizer are delivered into the combustion chamber from separate tanks at controlled rates and conditions, said fuel and oxidizer being hypergolic upon contact.

An additional object of the instant invention is to provide an improved method of operating a bipropellant liquid motor wherein the fuel and oxidizer are delivered into the combustion chamber from separate tanks and controlled rates and conditions, said fuel and oxidizer being hypergolic upon contact and giving a high specific impulse.

Further objects and advantages of the present invention will appear from the more detailed description set forth hereinbelow, it being understood that such more detailed description is for purposes of illustration and explanation only.

In accordance with the present invention, basic amines and compounds containing N-F bonds are introduced into the combustion chamber through separate lines and from separate storage tanks. The compounds referred to in this application as containing NF bonds are tetra- 3,442,081 Patented May 6, 1969 ice fiuorohydrazine adducts of ethylenically unsaturated compounds. These derivatives are prepared by the addition of one mole of tetrafiuorohydrazine to the ethylenic linkage as shown below.

Thus, in each case there will be a -NF group on each of the two carbon atoms that were connected by the double bond. In this application these compounds will be referred to as compounds containing NF bonds or NF compounds and in each case the tetrafiuorohydrazine adducts of an ethylenically unsaturated compound is intended unless otherwise stipulated. As will be disclosed hereinafter, it is possible to synthesize compounds having more than two difluoroamino substituents.

The compounds shown for illustration are l,2,3-tris(difiuoroamino) propane and 2,3-'bis(difiuoroamino) propyl formate. The complete synthesis of these two compounds will be given with the examples. These compounds are by no means the only two which will give the desired results, but serve to function as examples only.

The rate of reaction and the degree of combustion occurring upon combination of the basic amine and N-F compound depends upon the number of NF groups present, the basicity of the amine, and the temperature of the reactants. Spontaneous combustion is facilitated by increasing the number of NF groups present in the NF compounds. The more basic the amine the easier it is to achieve spontaneous combustion. In like manner an increase in the temperature of the reactants assists in the achievement of spontaneous combustion. It is to be understood that all three requirements are not needed in all cases. Strongly basic amines give spontaneous combustion upon contact with compounds with two or three NF groups at room temperatures. Amines that are not so strongly basic may require a temperature of 60 C. to 80 C. for spontaneous combustion with the same N-F compounds. It is also conceivable that weakly basic amines will function as bipropellant fuels in combination with N-F compounds when an ignition system is employed in the motor.

It can be seen from the preceding discussion that the only limitations on the amines used are the conditions of the reaction motor. If an ignition system is to be used, such amines as 64% hydrazine, anhydrous hydrazine, and 1,3-diamino-2-propanol may be employed. Such amines as 3,3 diaminodipropylamine, ethylenediamine, and triethylenetetramine are sutficiently basic to be hypergolic with NF compounds at moderate temperatures and function as propellants without need for increased temperatures or ignition systems. However, the amines specifically set forth herein are not meant to be inclusive but are for the lPUI'POSE of exe-mplification only.

In some cases it may be desirable to use a nitrated oxidizer in combination with the N-F compound. Tests have shown that the difluoroamino compounds can be added to the nitrated oxidizers without an exothermic reaction occurring. Therefore, the fluorine and nitrogen containing oxidizers may be stored in the same tank. Examples of these oxidizers are triethyleneglycol dinitrate, diethyleneglycol dinitrate, and a mixture by weight of nitroglycerin, 24% diethyl phthalate, and 1% 2-nitrodiphenylamine.

Thermochemical calculations indicate that combustion of amines with difluoroamino oxidizers or with difluoroamino compounds in combination with nitrated oxidizers can give specific impulse values ranging from 270 lbs. sec./lb. to 315 lbs. sec./lb. depending upon the composition involved and the stoichiometry of the ingredients. Calculations indicate the highest impulse is obtained by oxidation of the carbon to carbon monoxide (CO) and carbon dioxide (CO with the oxygenated oxidizer and converting the hydrogen to hydrogen fluoride (HF) with the fluorine oxidizer.

The following examples serve to further illustrate the invention without limiting it thereto.

EXAMPLE 1 Preparation of l,2,3-tris(difluoroamino) propane 1.5 ml. (0.01735 mole) of allyl bromide were placed in a liter flask and cooled in aDry Ice-acetone bath. The system was evacuated and 0.0347 mole N F was added. The mixture was heated for 3 hours at 145 C. The products were allowed to stand overnight in the reaction flask. The products were distilled by heating the reaction flask with a hot air bath and pumping the system through Dry Iceacetone and liquid nitrogen traps. The impure product contained in the Dry Ice-acetone trap was warmed to room temperature and washed with concentrated sulfuric acid. The 1,2,3-tris(difluoroamino) propane formed a separate layer at the top of the solution. This layer was decanted and distilled. The BF. was 127 C. at atmospheric pressure.

EXAMPLE 2 Synthesis of 2,3-bis(difluoroamino) propyl formate One milliliter of allyl formate was placed in a five-hum dred milliliter round bottom flask. The flask was connected to a glass vacuum manifold and cooled to 78 C. using a Dry Ice-acetone bath and then evacuated to a pressure of 1 mm. Hg or less and checked for leaks. Tetrafluorohydrazine was added until the pressure rose to approximately 200 mm. Hg (measured at 78 C.). The flask and its contents were then allowed to warm to room temperature and thereafter heated for four hours at a temperature which was maintained between 100 C. to 110 C. Excess gaseous tetrafluorohydrazine was removed. The product, 2,3-bis(difluoroamino) propyl formate was recovered by vacuum distillation at a pressure of one to two millimeters of mercury and a temperature of 35 C. to 40 C.

Analysis.-Calculated for C H O N F C, 25.25; H, 3.16; F, 40.0. Found: C, 24.25; H, 3.15; F, 38.85.

The 2,3-bis(difluoroamino) propyl formate was further analyzed by its infrared spectra which showed absorption bonds of 11.0 to 12.3 microns. This absorption is characteristic of the NF bond. The nuclear magnetic resonance spectra indicated the presence of two adjacent difiuoroamino groups with one group being on an end carbon atom.

EXAMPLE 3 Reaction of 1,2,3-tris(difluoroamino) propane with various types of amines 1,2,3-tris(difluoroamino) propane (0.05 cc.) was added to 0.20 cc. of each of the following compounds at a constant temperature of 60 C.:

'(a) 64% hydrazine (b) anhydrous hydrazine (c) 3,3'-diarninodipropylamine (d) ethylenediamine (e) 1,3-diamino-2-propanol (f) triethylenetetramine.

All of the above amines gave an exothermic reaction immediately upon coming in contact with the difluoroamino compound. Two of the amines, 3,3'-diaminodipropylamine and triethylenetetramine, gave a spontaneous combustion with the difluoroamino compound.

EXAMPLE 4 Example 3 was repeated at a constant temperature of 80 C. At this temperature ethylenediamine, as well as 3,3'-diaminodipropylamine and triethylenetramine, gave spontaneous combustion.

4 EXAMPLE 5 Example 4 was repeated at a constant temperature of 30 C. At this temperature 3,3-diaminodipropylamine gave spontaneous combustion.

EXAMPLE 6 Reaction of 2,3-bis(difluoroamino) propyl fol-mate with various types of amines 2,3-bis(difluoroamino) propyl formate (0.05 cc.) was added to 0.20 cc. of each of the follownig compounds at a constant temperature of 60 C.:

(a) 64% hydrazine (b) anhydrous hydrazine (c) 3,3-diaminodipropylan1ine (d) ethylenediamine (e) 1,3-diamino-2-propanol (f) triethylenetetramine.

All of the above amines gave an exothermic reaction immediately upon coming in contact with the difluoroamino compound. Two of the amines, 3,3'-diaminodipropylamine and triethylenetetramine, gave spontaneous combustion with the difluoroamino compound. Similar results were obtained at a constant temperature of C.

EXAMPLE 7 It was observed that l,2,3-tris(difluoroamino) propane is stable at 60 C. in the following nitrate esters:

(a) triethyleneglycol dinitrate (b) diethyleneglycol dinitrate (c) 75% nitroglycerin, 24% diethyl phthalate, 1% 2- nitrodiphenylamine (by weight).

Upon the addition of 3,3'-diaminodipropylamine to a mixture of 1,2,3-tris(difluoroamino) propane and each of the nitrate esters, a spontaneous combustion occurred. Similar results were obtained at 30 C.

EXAMPLE 8 It was observed that 2,3-bis(difluoroamino) propyl formate is stable at 60 C. in the following nitrate esters:

(a) triethyleneglycol dinitrate (b) diethyleneglycol dinitrate (c) 75% nitroglycerin, 24% diethyl phthalate, 1% 2- nitrodiphenylamine (weight percent).

Upon the addition of 3,3-diaminodipropylamine to a mixture of 2,3-bis(difiuoroamino) propyl formate and each of the nitrate esters, a spontaneous combustion occurred.

On the basis of the above examples, it may be expected that the reactions indicated would occur with all basic amines and with all compounds containing NF groups. The extent of the reaction will depend upon the conditions, basicity of the amine, and reactivity of the difluoroamino compound.

The preferred operating range as shown by the examples is 25 C. to C. At the lower temperatures (30 C.) 3,3-diaminodipropylamine is hypergolic upon contact with the difluoroamino compounds. At the higher temperatures (60 C.) triethylenetetramine is also hypergolic. At temperatures slightly higher (80 C.) ethylenediamine joins the other two as hypergolic fuels. Similar results are obtained when the nitrated oxidizers are used in combination with the difluoroamino compounds. It may also be expected that difluoroamino compounds and nitrated oxidizers can be stored together in the same container.

It is to be understood that the above examples are meant for purposes of illustration and that the invention is limited only by the appended claims.

We claim:

1. A method of operating a bipropellant liquid reaction motor which comprises bringing together in a combustion Zone of said motor a difluoroamino substituted compound selected from the group consisting of 1,2,3-tris(difluoroamino) propane and 2,3-bis(difluoroamino) propyl formate and a basic amine selected from the group consisting of 3,3-diaminodipropylamine, triethylenetetramine, and ethylenediamine hypergolic with said difluoroamino substituted compounds upon contact.

2. The method of claim 1 wherein the difiuoroamino substituted compound is 1,2,3-tris(difluoroamino) propane and the basic amine is 3,3-diaminodipropylamine.

3. The method of claim 1 wherein the difluoroamino substituted compound is 1,2,3;tris(difluoroamino) propane and the basic amine is triethylenetetramine.

4. The method of claim 1 wherein the difiuoroamino substituted compound is 1,2,3-tris(difluoroamino) propane and the basic amine is ethylenediamine.

5. The method of claim 1 wherein the difiuoroamino substituted compound is 2,3-bis(difluoroamino) propyl formate and the basic amine is 3,3-diarninodipropylamine.

6. The method of claim 1 wherein the difiuoroamino substituted compound is 2,3-bis(difluoroamino) propyl formate and the basic amine is triethylenetetramine.

7. The method of claim 1 wherein the difiuoroamino substituted compound is 2,3-bis(difluoroamino) propyl formate and the basic amine is ethylenediamine.

8. The method of operating a bipropellant liquid reaction motor which comprises bringing together a difluoroamino substituted compound selected from the group consisting of 1,2,3-tris(difluoroamino)propane and 2,3-bis (difluoroamino)-propyl formate; a nitrated oxidizer selected from the group consisting of tri-ethyleneglycol dinitrate, diethyleneglycol dinitrate, and a mixture of 75% by weight nitroglycerin, 24% by weight diethyl phthalate, and 1% by weight 2-nitrodiphenylamine; and a basic amine selected from the group consisting of ethylenediamine, triethylenetetramine, and 3,3'-diaminodipropylamine.

9. The method of operating a bipropellant liquid reaction motor which comprises bringing together in the combustion zone of said motor a tetrafiuorohydrazine adduct of an ethylenically unsaturated compound characterized by the presence of the group ()t-t N F2 N F2 and a strongly basic amine hypergolic with said adduct. 10. The method according to claim 9 wherein said basic amine is selected from the group consisting of ethylenediamine, triethylenetetramine, and 3,3'-diaminodipropylamine.

11. The method of claim 8 wherein the difluoroamino substituted compound is 1,2,3-tris(difiuoroamino) propane, the nitrated oxidizer is triethyleneglycol dinitrate, and said basic amine is 3,3'-dia rninodipropylamine.

12. The method of claim 8 wherein the difluoroamino substituted compound is l,2,3-tris(difiuoroamino) propane, the nitrated oxidizer is diethyleneglycol dinitrate, and said basic amine is 3,3'-diaminodipropylamine.

13. The method of claim 8 wherein the difluoroamino substituted compound is l,2,3-tris(difiuoroamino) propane, the nitrated oxidizer is a mixture of 75 nitroglycerin, 24% diethyl phthalate, and 1% 2-nitrodiphenylamine, and said basic amine is 3,3'-diaminodipropylamine.

14. The method of claim 8 wherein the difiuoroamino substituted compound is 2,3-bis(difiuoroamino) propyl formate, the nitrated oxidizer is triethyleneglycol dinitrate,

and said basic amine is 3,3-diaminodipropylamine.

15. The method of claim 8 wherein the difiuoroamino substituted compound is 2,3-bis(difiuoroamino) propyl formate, the nitrated oxidizer is diethyleneglycol dinitrate, and said basic amine is 3,3-diaminodipropylamine.

16. The method of claim 8 wherein the difluoroamino substituted compound is 2,3-bis(diflu0roamino) propyl formate, the nitrated oxidizer is a mixture by weight of 75% nitroglycerin, 24% diethyl phthalate, and 1% 2- nitrodiphenylamine, and said basi amine is 3,3'-diaminodipropylamine.

17. The method of operating a bipropellant liquid reaction motor which comprises bringing together in the combustion zone of said motor a mixture of a tetrafluorohydrazine adduct of an ethylenically unsaturated compound characterized by the presence of the group l am is UNITED STATES PATENTS l/l963 Rogers -35.4 X 8/1963 Hamrick et a1. 6035.4

OTHER REFERENCES Booth et al., Chem. Reviews, vol. 41, pp. 422 to 439 (1947).

BENJAMIN R, PADGETT, Primary Examiner.

US. Cl. X.R. 

1. A METHOD OF OPERATING A BIPROPELLANT LIQUID REACTION MOTOR WHICH COMPRISES BRINGING TOGETHER IN A COMBUSTION ZONE OF SAID MOTOR A DIFLUOROAMINO SUBSTITUTED COMPOUND SELECTED FROM THE GROUP CONSISTING OF 1,2,3-TRIS(DIFLUOROAMINO) PROPANE AND 2,3-BIS(DIFLUOROAMINO) PROPYL FORMATE AND A BASIC AMINE SELECTED FROM THE GROUP CONSISTING OF 3,3''-DIAMINODIPROPYLAMINE, TRIETHYLENETETRAMINE, AND ETHYLENEDIAMINE HYPERGOLIC WITH SAID DIFLUOROAMINO SUBSTITUTED COMPOUNDS UPON CONTACT. 